Sounds like another application is taking over the screen perhaps. Try setting the game to run in windowed mode maybe to help see what other app is taking control or reboot under selective startup mode to prevent other apps from auto-starting until you can figure out which it is.
MIMINIZES AT STARTUP
Help.
Sounds like another application is taking over the screen perhaps. Try setting the game to run in windowed mode maybe to help see what other app is taking control or reboot under selective startup mode to prevent other apps from auto-starting until you can figure out which it is.
https://us.battle.net/support/en/article/Closing-Background-Applications
To get D3 to use Windowed mode from outside the game, edit your D3Prefs.txt file located in the Documents\Diablo III folder.
Edit the line starting with "DisplayModeWindowMode"
to look like this
DisplayModeWindowMode "1"